Utility ground detection

ABSTRACT

In an embodiment, a missing utility ground detection circuit includes a pair of balanced resistors each connected to receive utility voltage from a different one of a pair of utility power lines, the balanced resistors being connected together at a summing node to be capable of summing the voltages from the pair of utility power lines. It includes an unbalance resistor connected to shunt voltage from one of the utility power lines. It has a summing amplifier with an input coupled to the summing node and to a reference voltage, and an input coupled to a second reference voltage. It has an averaging circuit connected at the output of the summing amplifier. A comparator is provided having an input connected to the averaging circuit an input connected to a threshold voltage.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/690,946, by Flack et al., entitled UTILITY GROUND DETECTION, filedNov. 30, 2012, which is a continuation of PCT Application No.PCT/US2011/038776, by Flack et al., entitled UTILITY GROUND DETECTION,filed 1 Jun. 2011, which claims the benefit of U.S. ProvisionalApplication No. 61/350,459, filed on Jun. 1, 2010, by Flack et al.,entitled UTILITY GROUND DETECTION, all herein incorporated by referencein their entireties.

BACKGROUND

One way to charge an electric vehicle is to supply the vehicle withutility power so that a charger in the vehicle can charge the battery inthe vehicle. If there is missing ground at the utility power, or it isnot supplied to the car, the car can become charged. If someone istouching car while grounded, that person could be shocked.

What is needed is a way to detect the absence of utility ground. In afurther embodiment what is needed is a way to detect the absence ofutility ground without false indications.

SUMMARY

In one possible embodiment, a missing utility ground detection circuitis provided which includes a pair of balanced resistors each connectedto receive utility voltage from a different one of a pair of utilitypower lines, the balanced resistors being connected together at asumming node to be capable of summing the voltages from the pair ofutility power lines. The missing utility ground detection circuitincludes an unbalance resistor connected so as to shunt voltage from oneof the utility power lines. The missing utility ground detection circuithas a summing amplifier with a first input coupled to the summing nodeand to a first reference voltage and a second input coupled to a secondreference voltage. The missing utility ground detection circuit has anaveraging circuit connected at the output of the summing amplifier. Acomparator is provided having a first input connected to the averagingcircuit a second input connected to a threshold voltage.

In some embodiments, the unbalance resistor may be connected between autility power line input and ground.

In some embodiments, the first input of the summing amplifier is alsoconnected to a reference voltage, which may be via an offset resistor.In some embodiments, the second input of the summing amplifier may beconnected to ground and the first input of the summing amplifierconnected to receive a positive reference voltage via an offsetresistor.

In other embodiments a diode, for example a Zener diode, may beconnected between first input of the summing amplifier and the balancedresistors. The diode may be in place of the reference voltage and offsetresistor.

In some further embodiments, the second input of the comparator may beconnected between threshold resistors, the threshold resistors beingconnected to each other in series, the threshold resistors beingconnected between ground and a reference voltage. In some embodiments, afeedback resistor may be provided connected between the second input ofthe comparator and an output of the comparator.

In one possible embodiment, a missing utility ground detection circuitis provided which includes a summing amplifier having the invertinginput connected to receive utility voltage via balanced resistors and areference voltage via a shunt connected offset resistor. Thenon-inverting input is connected to receive a reference voltage. Anunbalance resistor is connected in shunt between a utility power lineinput and a reference voltage. A filter is connected to the output ofthe summing amplifier. Also included is a comparator with the invertinginput connected to an output of the filter and the non-inverting inputconnected to receive a threshold voltage. An optional feedback resistormay be connected between the non-inverting input of the comparator andthe output of the comparator.

In some embodiments, the non-inverting input of the summing amplifier isconnected to ground and the inverting input of the summing amplifier isconnected to receive a positive reference voltage via the shuntconnected offset resistor.

In one possible embodiment, a missing utility ground detection circuitis provided which includes a summing amplifier having the invertinginput connected to received utility voltage via a Zener diode connectedin series with parallel connected balanced resistors each connected to autility power input. The non-inverting input is connected to a referencevoltage. An unbalance resistor is connected in shunt between a utilitypower line input and a reference voltage. A filter is connected to theoutput of the summing amplifier. Also included is a comparator with theinverting input connected to an output of the filter and thenon-inverting input connected to receive a threshold voltage. Anoptional feedback resistor may be connected between the non-invertinginput of the comparator and the output of the comparator.

In one possible implementation, a method is provided for detecting amissing utility ground in utility voltage inputs. The method may includeoffsetting one of the utility voltage inputs, sensing and summing theoffset utility voltage and the other of the utility voltage inputs, andcomparing the summed voltages to a threshold voltage to provide acompared output. The compared output is averaged. The averaged output isthen compared to a threshold voltage to provide a ground fault signal.

Some implementations, further include controlling a utility powercontactor using the ground fault signal as an input to determine whetherto at least one of open or close the utility power contactor so as to atleast one of supply or inhibit utility power to an AC output.

Some implementations include combining the summed voltages with anoffset voltage prior to comparing the summed voltages to a thresholdvoltage. In some implementations offsetting the voltage includesoffsetting with a positive voltage.

An alternate implementation includes rectifying the summed voltagesprior to comparing the summed voltages to a threshold voltage to providethe compared output. In some implementations, rectifying included usinga Zener diode.

In one implementation, the sensing is performed using balancedresistors.

In one implementation, averaging includes filtering the compared outputusing a series resistor and shunt capacitor.

Some implementations include feeding back a portion of ground faultsignal and combining it with the threshold voltage such that theaveraged output is compared to the combined threshold voltage andfeedback portion of the ground fault signal to provide the ground faultsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will be betterunderstood with regard to the following description, appended claims,and accompanying drawings where:

FIG. 1 shows a simplified schematic view of one possible embodiment ofthe missing utility ground detection circuit.

FIG. 2 shows a simplified schematic view of portion of the missingutility ground detection circuit of FIG. 1, showing balanced summingresistors for utility power L1 (AC_1) and L2 (AC_2), and an unbalanceresistor.

FIG. 3 shows a simplified schematic view of another possible embodimentof the missing utility ground detection circuit using a Zener diode.

FIG. 4 shows a schematic view of a cable to connect utility power to anelectric vehicle (not shown) along with some associated circuitry.

FIG. 5 shows a schematic view of a contactor control circuit.

FIG. 6 shows an enlarged more complete schematic of the pilot circuitryshown in partial schematic in FIG. 4.

DESCRIPTION

When the ground is a true ground it will read zero. When the ground is a3 phase midpoint (neutral), the neutral will fluctuate sinusoidally. Onepurpose of various embodiments of the missing utility ground circuit 10(FIG. 1) is to identify whether the midpoint of the voltages L1 and L2(FIG. 4) is tied to ground. The two voltages L1 and L2 represent the twophases with respect to ground/neutral. The two voltage sources L1 and L2are 180 degrees out of phase if it is single phase (240V), or 120degrees if it is three phase (208V). The signals AC_1 and AC_2 shown inFIG. 1 are the utility power voltages L1 and L2 (FIG. 4), respectively.

FIG. 1 shows a simplified schematic view of one possible embodiment ofthe missing utility ground detection circuit 10. Amplifier 200 isreferred to as a summing amplifier 200 herein because the invertinginput 2 of the amplifier 200 is a summing node, as discussed below. Thesumming amplifier 200 functions as a comparator as it is a single supplyamplifier with no feedback resistor, so has no net gain. If theinverting input 2 of the summing amplifier 200 is below thenon-inverting input 3 the output 1 goes high. If the inverting input 2of the summing amplifier is above the non-inverting input 3 the output 1goes low. In the embodiment shown in FIG. 1, VDC is 3.3V. As shown inFIGS. 1 and 3, VDC may be coupled to ground via a capacitor if desired,for example a 0.1 microfarad capacitor.

FIG. 2 shows a simplified schematic view of portion 10 b of the missingutility ground detection circuit 10 of FIG. 1, showing balanced summingresistors 130 and 140 for utility power L1 (AC_1) and L2 (AC_2), and anunbalance resistor 120. Shown in FIG. 2, the AC_1 signal is connected toground via unbalance resistor 120. The unbalance resistor 120 in thisexample is 60K ohms, which is shown as three 20 k ohm 1 Watt resistorsin series. The AC_1 and AC_2 signals are connected to the invertinginput 2 of the summing amplifier 200 via balanced sense resistors 130and 140, respectively. Thus, the AC_1 signal is connected to theinverting input 2 of the summing amplifier 200 via a balanced senseresistor 130, which is 3M ohms, shown as three 1M ohm resistors inseries in this example, and the AC_2 signal is connected to theinverting input 2 of the summing amplifier 200 via the balanced senseresistor 140, which is also 3M ohms, shown as three 1M ohm resistors inseries in this example. An offset resistor 50 is also connected betweenthe inverting input 2 of the summing amplifier 200 and the referencevoltage VDC. The offset resistor is 49.9K ohms and its reference voltageVDC is +3.3V in this example. The non-inverting input 3 of the summingamplifier is connected to ground.

When the missing utility ground circuit 10 is connected to three phaseutility power the summation does not add up to zero, but is shifted asmall amount. For higher voltage, i.e. 240V three phase, this can causean improper fault signal, AC_GND_FAULT. To inhibit an AC_GND_FAULT on asmall amount of sinusoidal voltage, and only indicate AC_GND_FAULT forthe larger amount of voltage characteristic of a missing utility ground,the offset resistor 50 is used to offset the measurement so that thereare not improper AC_GND_FAULT indications. The summing amplifier 200half wave rectifies the summation, and the offset resistor 50 offsetsthe voltage in the positive direction.

In operation, if there is no utility ground present, the unbalanceresistor 120 pulls the line voltage toward the ground/common of thecircuit, i.e. the circuit board ground. If there is no utility ground,the unbalance resistor 120 pulls the voltage at the inverting input 2 ofthe summing amplifier 200, it causes the output 1 of the summingamplifier 200 to pulse. A filter circuit 160 averages the pulses fromthe output 1 of the summing amplifier 200 and provides them tocomparator 300 (i.e. an operational amplifier functioning as thecomparator 300). The filter circuit 160 has a series resistor 162,connected in series with the inverting input 6 of the comparator 300.The filter 160 also has a capacitor 164 connected in parallel to groundbetween the resistor 162 and the inverting input 6 of the comparator300. In this example, the resistor 162 is 1 M ohm and the capacitor 164is 1 microfarad, to form a low pass filter.

The comparator 300 compares output of the filter 160 to a thresholdvoltage and if the output of the filter 160 crosses the thresholdvoltage, the comparator 300 provides the AC_GND_FAULT signal at theoutput 7 of the comparator 300. Threshold resistors 170 and 180 areconnected at their respective ends to ground and to a reference voltageVref (3.0V in this example), and the other ends are connected togetherand to the non-inverting input 5 of the comparator 300 to provide thethreshold voltage. The threshold resistors 170 and 180 are 3.65K ohmsand 49.9 K ohms, respectively. Thus, the non-inverting input 5 of thecomparator 300 is connected to ground via resistor 170 and to thereference voltage Vref via resistor 180.

A feedback resistor 190 is connected from the output 7 of the comparator300 to the non-inverting input 5 of the comparator 300. The feedbackresistor 190 introduces hysteresis in the comparison to shift thethreshold of detection, though in various embodiments the circuit 10will trip on the first occurrence of the fault which is then latched, sooscillation of the AC_GND_FAULT is not a factor in such embodiments. Inone embodiment, the feedback resistor 190 is 1 M ohm.

The offset resistor 50 pushes the output 1 of the summing amplifier 200toward ground so that the comparator 300 does not trip improperly onthree phase power that actually has a ground. As the supply voltagesincrease, i.e. 240V and above, the amplitude of the sinusoidal voltageincreases, which increases the likelihood of an improper AC_GND_FAULT.With three phase power of about 240V or greater, the circuit 10 wouldnot work reliably without the offset resistor 50.

The summing amplifier 200 and the comparator 300 may both be operationamplifiers, for example type LMV342IDR, supplied by Texas Instruments,of Dallas, Tex.

In the circuit 10, the specific values, or components may be varied. Inthe specific example discussed herein with provide an AC_GND_FAULT willoccur if the ground is missing, or is above about 200 K to 500 K ohms.

In an alternate embodiment (FIG. 3), a Zener diode 55 could be insertedbefore the inverting input of the summing amplifier 200, instead ofhaving the offset resistor 50 (FIG. 1). In such an embodiment, the Zenerdiode 55 would be inserted in series between the network of balancedsense resistors 130 and 140 and the inverting input 2 of the summingamplifier 200. Thus, the AC_GND_SNS signal from the would be passedthrough the Zener diode 55 prior to entering the inverting input 2 ofthe summing amplifier 200.

In yet another embodiment (not show), a detector, or indicator, i.e.board level jumper, dip switch, etc. may used to identify thecharacteristic of the utility power, i.e. 240, 208, three phase, singlephase, etc. If three phase 240V or greater is used, the voltage of theutility may be detected to determine whether the utility voltage is overa threshold level, i.e. there is a utility over voltage. If there is anovervoltage, the AC_GND_FAULT may not be valid and may be a false trip.

In various embodiments, the fact that an over-voltage may cause a falsetrip is an inconvenience, but is easily recoverable. When the falsemissing ground fault is detected, then the CPU (not shown) can determinewhether the over voltage may have caused it, and therefore handle thefault response differently. In various embodiments, this is a“collateral” fault detection in that both faults, missing ground andovervoltage, may be detected. The over voltage threshold for this faultcan be adjusted by component selection to make use of it, or extend it,more out of trip range.

Referring to FIGS. 1-6, in one of many possible embodiments, when theutility ground G (FIG. 4) is not present, the line to ground balance setup by the balanced resistive reference 130 (FIG. 2) and 140 (FIG. 2)will become unbalanced due to the resistive leg 120 (FIG. 2) across onephase to ground. This will create a non-zero voltage at the summing nodeat the inverting input 2 of the comparator 200 (FIG. 1), which willcharge up the reservoir capacitor 164 (FIG. 1) over time and trip thecomparator 300 (FIG. 1) to provide the AC_GND_FAULT (FIGS. 1 and 6). TheAC_GND_FAULT (FIGS. 1 and 6) signal may be used to latch thecontactor-disable flip-flop 652 (FIG. 6) and disable the contactordriver 570 (FIG. 5) from closing the contactor relay 140 (FIG. 571) andtherefore the contactor 440 (FIG. 4), the operation of which are furtherdisclosed in PCT Application PCT/US11/032576, filed Apr. 14, 2011,entitled GROUND FAULT INTERRUPT CIRCUIT FOR ELECTRIC VEHICLE, by Flack,which claims the benefit of Provisional Application Ser. No. 61/324,296,filed Apr. 14, 2010, entitled GROUND FAULT INTERRUPT CIRCUIT FORELECTRIC VEHICLE, by Flack, both herein incorporated by reference intheir entireties.

It is worthy to note that any reference to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment may beincluded in an embodiment, if desired. The appearances of the phrase “inone embodiment” in various places in the specification are notnecessarily all referring to the same embodiment. Further the feature(s)of various embodiments may be included in other embodiments.

The illustrations and examples provided herein are for explanatorypurposes and are not intended to limit the scope of the appended claims.This disclosure is to be considered an exemplification of the principlesof the invention and is not intended to limit the spirit and scope ofthe invention and/or claims of the embodiment illustrated.

Those skilled in the art will make modifications to the invention forparticular applications of the invention.

The discussion included in this patent is intended to serve as a basicdescription. The reader should be aware that the specific discussion maynot explicitly describe all embodiments possible and alternatives areimplicit. Also, this discussion may not fully explain the generic natureof the invention and may not explicitly show how each feature or elementcan actually be representative or equivalent elements. Again, these areimplicitly included in this disclosure. Where the invention is describedin device-oriented terminology, each element of the device implicitlyperforms a function. It should also be understood that a variety ofchanges may be made without departing from the essence of the invention.Such changes are also implicitly included in the description. Thesechanges still fall within the scope of this invention.

Further, each of the various elements of the invention and claims mayalso be achieved in a variety of manners. This disclosure should beunderstood to encompass each such variation, be it a variation of anyapparatus embodiment, a method embodiment, or even merely a variation ofany element of these. Particularly, it should be understood that as thedisclosure relates to elements of the invention, the words for eachelement may be expressed by equivalent apparatus terms even if only thefunction or result is the same. Such equivalent, broader, or even moregeneric terms should be considered to be encompassed in the descriptionof each element or action. Such terms can be substituted where desiredto make explicit the implicitly broad coverage to which this inventionis entitled. It should be understood that all actions may be expressedas a means for taking that action or as an element which causes thataction. Similarly, each physical element disclosed should be understoodto encompass a disclosure of the action which that physical elementfacilitates. Such changes and alternative terms are to be understood tobe explicitly included in the description.

Having described this invention in connection with a number ofembodiments, modification will now certainly suggest itself to thoseskilled in the art. The example embodiments herein are not intended tobe limiting, various configurations and combinations of features arepossible. As such, the invention is not limited to the disclosedembodiments, except as required by the appended claims.

What is claimed is:
 1. A missing utility ground detection circuitcomprising: a) a pair of balanced resistors each connected to receiveutility power from a different one of a pair of utility power lines, thebalanced resistors being connected together at a summing node to becapable of summing a utility voltage from the pair of utility powerlines; b) an unbalance resistor connected in parallel with one of thebalanced resistors from only one line of the pair of utility powerlines; c) a summing amplifier comprising: 1) a first input coupled tothe summing node; 2) a second input coupled to a second referencevoltage; and 3) an output; d) an averaging circuit connected at theoutput of the summing amplifier; and e) a comparator comprising a firstinput connected to the averaging circuit a second input connected to athreshold voltage.
 2. The circuit of claim 1, wherein the first input ofthe summing amplifier is further connected to a reference voltage. 3.The circuit of claim 2, wherein the unbalance resistor is connectedbetween the only one line of the pair of utility power lines input andground.
 4. The circuit of claim 2, wherein the first input of thesumming amplifier is connected to the reference voltage via an offsetresistor.
 5. The circuit of claim 2, wherein the second input of thecomparator is connected between threshold resistors, the thresholdresistors being connected to each other in series, the thresholdresistors being connected between ground and a reference voltage.
 6. Thecircuit of claim 5 further comprising a feedback resistor connectedbetween the second input of the comparator and an output of thecomparator.
 7. The circuit of claim 2 further comprising a feedbackresistor connected between the second input of the comparator and anoutput of the comparator.
 8. The circuit of claim 2, wherein the secondinput of the summing amplifier is connected to ground, and wherein thefirst input of the summing amplifier is connected to receive a positivereference voltage via an offset resistor.
 9. The circuit of claim 1further comprising a diode connected between the first input of thesumming amplifier and the balanced resistors.
 10. The circuit of claim9, wherein the diode is a Zener diode.
 11. The circuit of claim 9,wherein the unbalance resistor is connected between the only one line ofthe pair of utility power lines input and ground.
 12. The circuit ofclaim 9, wherein the second input of the comparator is connected betweenthreshold resistors, the threshold resistors being connected to eachother in series, the threshold resistors being connected between groundand a reference voltage.
 13. The circuit of claim 12 further comprisinga feedback resistor connected between the second input of the comparatorand an output of the comparator.
 14. The circuit of claim 9 furthercomprising a feedback resistor connected between the second input of thecomparator and an output of the comparator.
 15. A missing utility grounddetection circuit comprising: a) a summing amplifier comprising: (i) aninverting input connected to receive utility voltage via balancedresistors and a reference voltage via a parallel connected offsetresistor; (ii) a non-inverting input connected to receive a referencevoltage; (iii) an output; b) an unbalance resistor connected in parallelwith one of the balanced resistors between only one utility power lineinput and a reference voltage; c) a filter having an input connected tothe output of the summing amplifier; and d) a comparator comprising: (i)an inverting input connected to an output of the filter; and (ii) anon-inverting input connected to receive a threshold voltage.
 16. Thecircuit of claim 15, a feedback resistor connected between thenon-inverting input of the comparator and an output of the comparator.17. The circuit of claim 15, wherein the non-inverting input of thesumming amplifier is connected to ground, and wherein the invertinginput of the summing amplifier is connected to receive a positivereference voltage via the parallel connected offset resistor.
 18. Thecircuit of claim 15, wherein the unbalance resistor is connected betweenthe only one utility power line input and ground.
 19. The circuit ofclaim 15, wherein the non-inverting input of the comparator is connectedbetween threshold resistors, the threshold resistors being connected toeach other in series, the threshold resistors being connected betweenground and a reference voltage.
 20. A missing utility ground detectioncircuit comprising: a) a summing amplifier comprising: (i) an invertinginput connected to receive utility voltage via a Zener diode connectedin series with parallel connected balanced resistors each connected to autility power input, respectively, the Zener diode being connected inseries between the inverting input and the parallel connected balancedresistors; (ii) a non-inverting input connected to a reference voltage;and (iii) an output; b) an unbalance resistor connected between only oneutility power line input and a reference voltage; c) a filter having aninput connected to the output of the summing amplifier; and d) acomparator comprising: (i) an inverting input connected to an output ofthe filter; and (ii) a non-inverting input connected to receive athreshold voltage.
 21. The circuit of claim 20 further comprising afeedback resistor connected between the non-inverting input of thecomparator and an output of the comparator.
 22. The circuit of claim 20,wherein the non-inverting input of the summing amplifier is connected toground.
 23. The circuit of claim 20, wherein the unbalance resistor isconnected between the only one utility power line input and ground. 24.The circuit of claim 20, wherein the non-inverting input of thecomparator is connected between threshold resistors, the thresholdresistors being connected to each other in series, the thresholdresistors being connected between ground and a reference voltage.
 25. Amethod for detecting a missing utility ground in utility voltage inputs,the method comprising: a) unbalancing only one of the utility voltageinputs; b) sensing and summing the unbalanced only one of the utilityvoltage inputs and an other of the utility voltage inputs; c) comparingthe summed voltages to a reference threshold voltage to provide acompared output; d) averaging the compared output to provide an averagedoutput; and e) comparing the averaged output to a fault thresholdvoltage to provide a ground fault signal.
 26. The method of claim 25,further comprising feeding back a portion of ground fault signal andcombining the feedback portion with the fault threshold voltage suchthat the averaged output is compared to a combined signal comprising thefault threshold voltage and the feedback portion to provide the groundfault signal.
 27. The method of claim 25, wherein the sensing isperformed using balanced resistors.
 28. The method of claim 25, whereinaveraging comprises filtering the compared output using a seriesresistor and shunt capacitor.
 29. The method of claim 25, furthercomprising combining the summed voltages with an offset voltage prior tothe comparing of the summed voltages to the reference threshold voltageto provide the compared output.
 30. The method of claim 29, whereinoffsetting the voltage comprises offsetting with a positive voltage. 31.The method of claim 30 further comprising controlling a utility powercontactor using the ground fault signal as an input to determine whetherto at least one of open or close the utility power contactor so as to atleast one of supply or inhibit utility power to an AC output.
 32. Themethod of claim 25 further comprising passing the summed voltagesthrough a Zener diode prior to the comparing of the summed voltages tothe reference threshold voltage to provide the compared output.
 33. Themethod of claim 32 further comprising controlling a utility powercontactor using the ground fault signal as an input to determine whetherto at least one of open or close the utility power contactor so as to atleast one of supply or inhibit utility power to an AC output.
 34. Themethod of claim 25, further comprising controlling a utility powercontactor using the ground fault signal as an input to determine whetherto at least one of open or close the utility power contactor so as to atleast one of supply or inhibit utility power to an AC output.